Hi,
base system model is something like first boot which ensure basic
settings after first login to rest-service of target machine.
First I describe how it should look from user perspective. User login
to target machine and then he see first module from first boot sequency,
after saving settings go to next step until last one is complete and
then show standard control panel.

Yes, thats how I also understand the feature request.

Ideally, the modules to call and their ordering is freely configurable
so vendors can add and remove modules as needed.

Implementation proposal: Create new rest-service for first boot. This
module store in database last successfully saved module. It also
contains list of modules and its order. So frontend ask only what module
is next one. If next one is control panel, then first boot is complete
passed.

I do not think that this requires a REST service. Calling configuration
modules in a specific order is pure client side (web ui) functionality
imho.

Frontend is implemented mostly in control panel. It ask backend for
next module in first boot order. If next module is not control panel,
then control panel redirect to that module.

Keeping it all in the frontend should be sufficient. Are there any
specific requirements for using the backend here ?

The most complicated think is how recognize, that module settings is
successfully set. My proposal is set to session in control panel, that
modul must set status.

A 'configuration needed' status belongs to the (REST)service, not to
the session. The backend service is the authorative source of this
state information.